The invention disclosed herein is generally related to the method of elemental chemical analysis known as neutron activation. More particularly, this invention is related to methods and apparatus for irradiating a flowing fluid with neutrons. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
Briefly, in neutron activation analysis a sample to be analyzed for its elemental composition is irradiated with neutrons to produce various radioactive activation products. The particular species of activation products produced are uniquely determined by the elemental composition of the sample. The subsequent decay of the activation products is accompanied by emission of characteristic gamma rays, neutrons and other types of radiation, which is analyzed by spectrophotometric techniques to determine the identities and concentrations of the activation products. From this information, the elemental composition of the sample can be determined.
In one application of this method, fissile materials in a sample are assayed by irradiating the sample with thermal neutrons to induce fission of the fissile materials. The fission is accompanied by prompt as well as delayed emission of neutrons and gamma radiation. These radiations are analyzed to determine the content of fissile materials in the sample.
Neutron irradiation of a sample may be accomplished in several ways. Most commonly, a sample aliquot is placed in a region of high neutron flux in a nuclear reactor. Alternatively, a sample may be irradiated by exposing it to a radioactive neutron source such as Californium-252 (.sup.252 Cf). The present invention is directed to the latter type of irradiation.
There has existed a need for a simple and efficient method of irradiating a continuously flowing stream of solution, for example solutions flowing in a chemical processing plant. Such irradiation could be coupled with downstream detection of delayed radiation (gamma rays or neutrons) by an appropriate detector so as to provide continuous, real-time analysis of the solution. Such a method of neutron activation analysis would have several advantages over the conventional method of removing a sample aliquot for analysis. First, the elemental composition of the flowing solution could be monitored in real-time, thus eliminating the usual delay between the taking of an aliquot and the analysis of its composition. Also, variations in the elemental composition with time could be detected and accurately measured. Further, all of the material in a process stream would be analyzed, as opposed to analysis of selected aliquots of the process stream such as is obtained by conventional neutron activation methods. Appropriate integration of temporal variations in a process stream would enable accurate material accounting of the various elements in the stream. Finally, continuous real-time monitoring of the elemental composition in a process stream could provide a basis for feedback-controlled regulation of the chemical process or processes being carried out upstream.
There are several factors to be considered with regard to the irradiation of a process stream with a neutron source such as .sup.252 Cf. First, it is desirable that the neutron source be in close proximity to the flowing stream so as to obtain optimum utilization of the source. Also, it is desirable that the neutron source be positioned within the process stream so as to uniformly irradiate all parts of the process stream, and also to make the most efficient use of the source, which emits neutrons in all directions uniformly. At the same time, however, it is desirable to be able to remove the neutron source from the process stream, for example to service or replace the source, without interrupting the flow of the stream or breaching the containment of the stream.
Accordingly, it is the object and purpose of the present invention to provide an apparatus for irradiating a fluid flowing in a process stream. More particularly, it is an object to provide an apparatus for neutron irradiation of flowing fluid.
It is also an object of the invention to provide such an apparatus wherein the radiation source is removable from the process stream without interrupting the flow of the stream or breaching the primary containment of the flow path.
It is another object of the present invention to provide an apparatus for irradiating a process stream wherein the radiation source is positioned so as to obtain optimum geometrical efficiency of irradiation.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.